In my opinion, the Tau are one of the most interesting. They have a relatively new and different ideology compared to other factions. They believe in the 'Greater Good' and are trying to unite the galaxy under their banner in a more diplomatic way at times. The Necrons are also fascinating. They are ancient robotic - like beings that were once a great civilization and now are awakening from their long slumber. And of course, the Dark Eldar, with their cruel and sadistic ways of obtaining souls to survive, add a lot of dark flavor to the Warhammer 40k universe.
The Space Marines are really cool. They are super - strong, genetically enhanced warriors, highly disciplined and often the heroes in many stories. Another interesting one is the Orks. They are a rowdy and war - loving race, always looking for a good fight and having a very unique, crude culture. And the Eldar, with their advanced technology and complex society, are also quite fascinating.
Well, the Tyranids are very interesting in Warhammer 40k fiction. They are a race of bio - engineered aliens that exist only to consume all other life forms. Their hive - mind nature and the way they adapt to different situations is quite unique. Then there are the Chaos Space Marines. These are former Space Marines who have turned to the Chaos Gods, and they bring a lot of dark and edgy elements to the stories. Also, the Imperial Guard, with their vast numbers and gritty determination in the face of overwhelming odds, is an interesting faction.
The Inquisitors can be very interesting characters in Warhammer 40k Fanfiction. They have this power to hunt down heretics and xenos, and their investigations can lead to all kinds of crazy adventures. Some Inquisitors are on the edge of heresy themselves, which adds a layer of complexity and intrigue to their stories.
One interesting Warhammer 40k fan fiction is about a group of Space Marines who find themselves on a lost planet filled with ancient technology. They have to battle against not only the local xenos but also the temptation of the powerful and often dangerous technology. It's a great story as it shows the moral and physical challenges they face.
The plotline about the Dark Angels Space Marine chapter is also captivating. They have a dark secret in their past related to the Fallen Angels. They are constantly on a quest to redeem themselves while still serving the Imperium. And the story of the Sisters of Battle, a female - only military order in the Imperium, is full of tales of faith, combat, and loyalty.
The character interactions are really interesting. Imagine Harry Potter meeting a Space Marine or a Chaos Sorcerer. How would they communicate? How would their different moral compasses and worldviews clash? These fanfictions explore such interactions in great detail. For example, a story might show Harry trying to convince a Space Marine that magic can be a force for good, while the Space Marine is skeptical due to the corrupting influence of chaos in his own universe. It makes for some really engaging reading.
I think 'Fulgrim' is also a well - known Warhammer 40k novel. It delves deep into the story of the Primarch Fulgrim. We get to see his fall from grace, how he was corrupted by chaos. It's a tragic story that shows how powerful and yet vulnerable the Primarchs can be in this complex universe.
Marneus Calgar of the Ultramarines is very memorable. He is a powerful and respected Space Marine chapter master. Another is Abaddon the Despoiler, the leader of the Chaos Space Marines. His actions are central to many of the Chaos - related plotlines.
One interesting concept is the Tyranid's extreme adaptability. In fan fiction, they can quickly evolve to counter any threat they face, like developing new bio - weapons against a particularly tough enemy. Another is their hive mind, which is often explored in more depth, showing how individual Tyranids are just parts of a greater, all - knowing entity.
The space battles are often the highlight. Warhammer 40k has huge fleets of gothic - looking ships armed with massive guns and torpedoes. Star Trek has its own sleek starships with advanced weaponry like photon torpedoes and phasers. In fanfiction, a large - scale battle between a Warhammer 40k imperial fleet and a Star Trek Federation fleet would be amazing. The different tactics, ship designs, and crew capabilities would all come into play. For instance, the hierarchical and often fanatical nature of the Warhammer 40k crews compared to the more diverse and diplomatic Star Trek crews would lead to very different decision - making processes during the battle.
One interesting idea could be a story where the Space Marines from Warhammer 40k team up with the Avengers. Picture the Ultramarines and Captain America leading a combined force against a chaos incursion in New York. The Ultramarines' discipline and advanced weaponry combined with the Avengers' superpowers would make for an epic battle.
The Hive Tyrant is often a popular character. It's a powerful leader in the Tyranid swarm, and in fan fiction, it can be depicted as having unique strategies and abilities. Another one is the Zoanthrope, with its psychic powers being a focus in many stories.